Conventionally, an excimer discharge lamp has been used as an ultraviolet ray light source for a photochemical reaction, such as photo-cleaning, surface alteration and sensitization of a chemical substance. For example, rare gas (such as xenon) and halide (such as fluoride), which are enclosed in this excimer discharge lamp, are known as light emission gas. Halogen or halide is ionized at time of lamp lighting, so as to serve as halogen ions, and the reactivity thereof to other substances becomes very high. For this reason, an electric discharge container encloses the halogen or halide of an excimer discharge lamp must take appropriate measures. Japanese Patent Application Publication No. 06-310106 teaches such an excimer discharge lamp that takes such measures.
FIG. 10 is an explanatory cross sectional view of part of the excimer discharge lamp 9 disclosed in the Japanese Patent Application. The excimer discharge lamp 9 is equipped with an electric discharge container 91, titanium caps 911 provided in both ends of the electric discharge container 91, and metal nets 931 and 932 that are provided on an outer face of the electric discharge container 91 so as to be apart from each other.
The electric discharge container 91 is sealed by the titanium caps, using an O ring 921 made of fluorine contained resin system, so that an airtight electrical discharge space is formed inside the electric discharge container 91. This electrical discharge space is filled up with xenon gas and chlorine as electric discharge gas.
A power supply, which is not illustrated in the figure, is connected to the metal nets 931 and 932, and a high voltage of a high frequency is impressed to start the electric discharge. In the electrical discharge space, excimer electric discharge arises and ultraviolet rays with a wavelength band of 300 to 320 nm resulting from the xenon and chlorine are acquired. Since the sapphire pipe 91 has ultraviolet-rays permeability, the lamp emits the ultraviolet rays to the outside of the lamp 9 by the excimer electric discharge.
In the above-mentioned excimer discharge lamp 9, in order to enclose the electric discharge gas in the electrical discharge space, it is necessary to form a chip pipe in the titanium cap 911. Therefore, an excimer discharge lamp shown in FIG. 11, which is an overall view thereof, can be considered.
In FIG. 11, different portions from FIG. 10, will be described below, while similar portion descriptions will be omitted. The chip pipe 94 that leads to the electrical discharge space is connected to the titanium cap 911 provided at one end of the electric discharge container 91 by brazing or other method. Electric discharge gas is enclosed in the electrical discharge space through the chip pipe 94. After enclosing it, in order to seal the electrical discharge space, the chip pipe 94 is cut off for sealing, thereby forming the sealing portion 941 shown in FIG. 11. Material, such as a metal, that be cut off for sealing is used for the chip pipe 94.
When lighting the excimer discharge lamp 9 shown in FIG. 11, electric discharge sometimes does not occur between the pair of metal nets 931 and 932. This variable electric discharge results from an electric discharge arising between the one metal net 931 and the chip pipe 94, because the chip pipe 94 has a low voltage with respect to the one metal net 931.
Japanese Patent Application Publication No. 06-310106 teaches that although the cap 911 may be manufactured with high purity alumina, since the chip pipe 94 must be able to be cut off for sealing, it must be manufactured with metal material. Since electric discharge arises at least between the one metal net 931 and the chip pipe 94, the chip pipe 94 is heated, so that the thermal expansion difference occurs at the brazed portion between the cap 911 and the chip pipe 94 so that it may be damaged. Moreover, even though the portion between the cap 911 and the chip pipe 94 is not damaged, when the chip pipe 94 is heated, the O ring 922 is heated through the cap 911, so that the O-ring 922 deteriorates whereby airtightness of the electric discharge container 91 may not be maintained.